Truck unloader

ABSTRACT

A loading and unloading apparatus for a freight-carrying vehicle having a low-friction bed to enable loads to be positioned along the length of the vehicle bed with ease. The device includes an unloading unit which is located forwardly of the load and is slidable along the length of the bed. When the vehicle is unloaded, the unloading unit is driven rearwardly to urge the loads toward the rear of the vehicle. The unloading unit is driven by an endless chain disposed beneath the vehicle bed for movement along a run that extends lengthwise of the bed. The chain and unloading unit are connected during normal loading operations and advance forwardly in unison to the forwardmost end of the bed. When the unloading unit has advanced to the forward end of the bed it automatically disengages the chain to permit continued forward advancement of the chain and loading of the vehicle. Loading is facilitated by a removable loading unit which is connected manually to the chain and which engages the rearward end of the load to advance the load forwardly in unison with the chain. Because the unloading unit disengages the chain at its forwardmost position, the chain may be driven continually in a forward, loading direction to continue to load the vehicle. Additionally, the loading unit may be manually disengaged from and repositioned along the chain.

United States Patent [72] Inventor Emerson T. Oliver Marblehead, Mass.(Essex Engineering & Mfg. Inc., Day St., Lynn, Mass.)

[211 App]. No. 862,886

[22] Filed Oct. 1, 1969 [45] Patented Mar. 30, 1971 [54] TRUCK UNLOADER14 Claims, 7 Drawing Figs.

52 u.s.c1 214/516,

104/172; 198/224 51 Int.Cl. B60pl/38 so FieldofSearch 214/516,

Pri r na iyE xdmiiie r Albert .l. Makay Attorney-Kenway, Jenney &Hildreth ABSTRACT: A loading and unloading apparatus for afreightcarrying vehicle having a low-friction bed to enable loads to bepositioned along the length of the vehicle bed with ease. The deviceincludes an unloading unit which is located forwardly of the load and isslidable along the length of the bed. When the vehicle is unloaded, theunloading unit is driven rearwardly to urge the loads toward the rear ofthe vehicle.

The unloading unit is driven by an endless chain disposed beneath thevehicle bed for movement along a run that extends lengthwise of the bed.The chain and unloading unit are connected during normal loadingoperations and advance forwardly in unison to the forwardmost end of thebed. When the unloading unit has advanced to the forward end of the bedit automatically disengages the chain to permit continued forwardadvancement of the chain and loading of the vehicle. Loading isfacilitated by a removable loading unit which is connected manually tothe chain and which engages the rearward end of the load to advance theload forwardly in unison with the chain. Because the unloading unitdisengages the chain at its forwardmost position, the chain may bedriven continually in a forward, loading direction to continue to loadthe vehicle. Additionally, the loading unit may be manually disengagedfrom and repositioned along the chain.

Patented March 30, 1971 3,572,563

4 Sheets-Sheet 5 76 1 0 0 0 H h G v -68 32 I11 III I A j I xwxwllx JFIG.5

INVENTOR. EMERSON T OLIVER ATTORNEYS Patented March 30, 1971 3,572,563

4 Sheets-Sheet 4 lNVfENTOR. EMERSON T. OLIVER ATTORNEYS raucx UNLOADERSUMMARY OF THE INVENTION My invention relates to material handling and,more particularly, to improvements in loading and unloading of materialsfrom freight carrying vehicles such as trucks, planes, ships, and thelike.

Improved material handling techniques have resulted in the utilizationof low-friction conveyors in truck beds and other load carrying vehiclesto simplify the loading and unloading of material or to reposition theload along the truck bed. This technique is advantageous particularlywhen handling heavy, bulky loads and enables the load to be handled morequickly and with greater safety. For example, one of the techniquesfrequently employed is to provide a number of rows of roller conveyorsextending along the length of the truck bed. The rollers may beretractable to a position beneath the bed, as described in U.S. Pat. No.3,243,029, so that after the load has been positioned along the lengthof the truck bed, the rollers may be retracted and the load will restdirectly and firmly on the truck bed.

A number of techniques have beenemployed in handling loads with vehicleshaving low-friction beds. In order to overcome the obviousinefficiencies of manual loading and unloading, a number of mechanicalaids have been proposed in the art. In general these devices includemechanical pushing elements which are driven forwardly and rearwardlyalong the length of the vehicle to perform a loading and unloadingfunction. The pusher elements engage the containers or loads and urgesthem to the desired position along the vehicle bed. With these devicesit has been necessary to employ auxiliary controls to terminate movementof a pushing unit after it has been advanced to a predetermined positionalong the vehicle bed. For example, microswitches may be'employed tosense the presence of the pusher unit at one extreme end of its path oftravel to terminate further advancement of the pusher unit and precludejamming of the pusher unit or its drive mechanism. These prior devices,however, occasionally present some difficulty in that if the drivemechanism for the pusher unit is not stopped precisely when required thedevice may be damaged or may become jammed. It is necessary thereforethat these devices operate with a relatively high degree of precision toensure that the pushing function will terminate exactly when desired.Because of the generally rough conditions under which these devices mustfunction it has been difiicult to provide a device which operates withprecision and yet which has a high degree of reliability. It is amongthe primary objects of my invention to provide a loading and unloadingdevice for a vehicle of the type described which overcomes the foregoingdifficulties and is of simple rugged construction yet which functionswith the desired degree of precision and reliability.

In brief, my invention employs a continuous, endless chain supportedbeneath the vehicle bed. The chain is driven by sprockets arranged todrive the chain along an upper run at a level that is just below thebed. The upper run extends forwardly and rearwardly along the length ofthe vehicle bed and a slot is formed in the bed to-expose the upper runof the chain. The sprockets are driven by a reversible motor to enablethe upper run of the chain to be driven either forwardly in a loadingdirection or rearwardly in an unloading direction beneath the slot. I

A loading unit and an unloading unit are disposed above the bed and aredriven by the chain for loading and unloading the vehicle. The unloadingunit is intended to be positioned forwardly of the load to engage theforwardmost end of the load. The unloading unit includes a number ofdownwardly extending teeth which protrude through the slot in the bedinto driving engagement with the exposed, upper run of the chain. Whenthe unloading unit is between either the extreme forward or rearward endof the upper run, it is driven forwardly or rearwardly in unison withthe chain. As described below in further detail the unloading unit isdisengaged automatically pun from the chain when it has been advanced toeither extreme forward or rearward end of the upper chain run.

The separate loading unit also includes a number of teeth engageablewith the upper run of the chain so that it too may be driven by thechain. The loading unit is intended to engage the rearward end of a loadplaced on the bed so that forward advancement of the chain will causethe loading unit to urge the load forward into the vehicle. After aparticular load has been moved to a desired forward position, theloading unit then is removed manually from engagement with the chain toenable a subsequent load to be placed on the rear position of the bed.The loading unit then is reconnected to the chain rearwardly of the newload to urge the new load forwardly into the vehicle. This process iscontinued until the vehicle is loaded as desired. As the vehicle isloaded and the chain and the unloading unit advance forwardly along thebed, the unloading unit may reach the extreme forward end of the chainrun. The automatic disengagement of the unloading unit permits the chainto be advanced thereafter in a loading direction to enable the loadingprocess to be completed without it jamming or damaging the unloadingunit or other elements of the device. Both the loading and unloadingunits include pusher plates which extend laterally over the conveyormeans for engagement with the load.

When my device is employed, as described herein, with a low-frictionconveyor, it will be appreciated. that relatively bulky and heavy loadsmay be moved along the conveyor with minimal force. Thus the loading andunloading units need not be bulky and occupy relatively little space.Because of the relatively small, compact nature of the device, it doesnot interfere with close and efficient compacting of the load within thevehicle.

Also among the objects of my invention is to provide a loading andunloading device for a freight carrying vehicle which is of simpleconstruction and which may be manufactured at a relatively low cost.

Another object of my invention is to provide a device for loading andunloading a vehicle which may be controlled, in its operation, from alocation external of the cargo space of the vehicle and which does notrequire, the presence of the vehicle driver or other person within thecargo space to position the freight. 1

Another object of my invention is to provide a device for automaticallyloading and unloading a freight carrying vehicle which, by reason of itssimplicity, may be added to existing vehicle as an accessory or whichmay be built into such vehicles at the time of their construction.

These and other objects and advantages of my invention will be apparentfrom the following detailed description of my invention with referenceto the accompanying drawings in which:

FIG. I is an illustration of a truck in which the bed is provided withretractable roller conveyors and which employs the loading and unloadingdevice in accordance with the invention;

FIG. 2 is a side elevation, partly in section, of the deviceillustrating the disengaged unloading unit;

FIG. 3 is an end view in section of the rearward end of the invention asseen along the line 34 of FIG. 2;

FIG. 4 is an end view of the forward end of my device as viewed from theline 4-4 of FIG. 2;

FIG. 5 is a side elevation, in section, illustrating the pusher unit infull engagement with the chain;

FIG. 6 is a view of the portable loading bar; and

FIG. 7 is a sectional view of the pusher unit as seen along the line 7-7of FIG. 5.

As shown in FIG. '1, a vehicle such as a truck body 10 having a bed 12is provided with a number of conveyor rows 14, each conveyor rowconsisting of a number of rollers 16 mounted along the length of eachconveyor row 14. The rollers 16 may be retractable as described above.The number of conveyor rows 14 and the lateral spacing between rows maybe varied according to the dimensions of the vehicle bed 112 and thetypes of loads to be carried. The arrangement shown in FIG. 1, in whichtwo pairs 18, 20 of conveyor rows 14 are provided, is suitedparticularly for use with palletized loads, so that each of the conveyorpairs 18, 20 may support a row of pallets on which the loads arecarried. This arrangement enables two rows of palletized loads to becarried within the truck body 10. It should be understood that althoughmy invention is described herein with reference to the'arrangement shownin FIG. 1, it may be employed with any arrangement of conveyor rows 14.

As shown more clearly in FIGS. 3 and 7, the bed 12 is provided with aslot 22 extending along the centerline of the truck in parallel to theconveyor rows 14. In the illustrative embodiment of the invention, theadjacent inner conveyor rows 14 of each conveyor pair 18, 20 are. spacedin close proximity to each other and, in this case, the slot 22 may beformed directly between the conveyor rows 14 themselves. Achannel-shaped incasement 24 is located beneath the bed 12 and may besupported on any of the rigid members of the vehicle, such as thecrossmembers 26. The incasement 24, which has an upper slot 28 formedalong its length, is disposed along the centerline of the vehicle bodyso that the upper slot 28 is in registry with the slot 22 formed in thebed 12 between the inner conveyor rows 14. The incasement 24 includes abottom wall 30 and sidewalls 32 which define a secondary guideway 34between the incasement 24 and an inverted channel-shaped member 36 whichis secured to the bottom wall 30 of the incasement 24. The secondaryguideway 34 serves to channel or guide the lower return run of anendless drive member such as a chain 38. The portion of the interior ofthe incasement 24 which is above the channel 36 serves to guide theupper run of the chain 38 which is exposed through the registered slots22, 28 formed in the incasement 24 and bed 12.

The drive for the endless chain 38 includes a drive sprocket 40, whichis driven by a motor 42 through the clutch 44. The driving mechanismpreferably is located at the rear of the truck and is supported from amounting plate 46 which in turn is secured to a rigid member of thevehicle body 10 beneath the bed 12. The upper and lower runs of thechain 38 are guided to their respective levels above and below thechannel member 36 by means of idler sprockets 48 and 50 which arerotatably supported between the sprocket supports 52. The sprocketsupports 52 are secured to and extend upwardly from the mounting plate46 and extend through a receptive opening 54 formed on the bottom wall30 of the incasement 34. Suitable holes 56 are formed in themounting'piate 46 to enable the upper and lower runs of the chain 38 topass therethrough and engage the drive sprocket 40. The forward end ofthe chain 38 passes about an idler roller 58 (see FIG. 4) which issupported rotatably between bearing blocks 60 located at the forward endof the incasement 24. The extremities of the upper run of the chain aredefined, therefore, by the sprocket 48 and roller 58. Thus, the chain 38is supported so that its upper run may be driven along a path conformingto that along which the load is to be moved. The motor 42 is reversibleso that the exposed upper run of the chain 38 may be driven either in aforward loading direction or in a rearward unloading direction asdesired.

An unloading unit 62 having laterally extending pusher elements orpusher plates 64 is associated with the chain 38, and may be drivenalong the length of the vehicle bed. The plates 64 of the pusher unit 62extend over the adjacent conveyor rows 14 for engagement with theforward end of a load or pallet supported on the conveyor rows '14. Theunloading unit 62 includes a retaining member or slide'66 disposedwithin the incasement 24 and which is slidably supported on the span 68of the channel 36. As shown more clearly in FIGS. 5 and 7, the slide 66includes a channel 70 formed along its length which receives, freely, aportion of the upper run of the chain 38. The lower portion of the slide66, which bears on the span 68 of the channel 36, is provided withinwardly directed flanges 72 to ensure that the chain 38 is retainedwithin the channel 70. The channel 70 is dimensioned to pennit the slide66 to pass freely over the chain 38. Additionally, the slide 66 is widerthan the widthwise dimension of the upper slot 28 in the incasement 24to preclude upward withdrawal of the slide 66 from the incasement 24 andseparation of the chain 38 and slide 66.

The slide 66 also includes a rib 72 formed integrally along its lengthwhich extends upwardly through the registered slots 28, 22 to projectabove the level of the bed 12. A vertical slot 74, formed lengthwisealong the rib 72, provides access to that portion of the upper run ofthe chain 38 which is disposed within the channel 70 of the slide 66.The slot 74 is respective to a number of downwardly projecting teeth 76formed integrally with and at the bottom of a central plate 78. Thus,the teeth 76 may mesh with the chain 38 and be advanced in unisontherewith.

The rearward, lower corner of the central plate 78 is pivoted to therearward end of the slides 66 at the pin 80 to enable the plate 78,pusher element 64 and teeth 76 to pivot upwardly (counterclockwise asseen in FIG. 2 and 5) out of engagement with the drive chain 38. It isimportant to note that the pivot pin 80 is disposed at a level which isabove the level at which the teeth 76 engage the upper run of the chain38. In accordance with the invention, the teeth 78 are disengaged fromthe chain when the unloading unit has been driven toward either itsforward or rearward extremity of the upper chain run. For example, asthe unloading unit 62 approaches the forward end of the chain run theforward end of the slide 66 will abut against the rearward end of thebearing blocks 60 to terminate forward movement of the slide 66 and,therefore, the entire unloading unit 62. Continued movement of the upperrun of the chain in a forward loading direction acts on the teeth belowthe level of the pin 80 to impart a moment to the plate 78(counterclockwise as seen in FIG. 2). This causes the plate 78, pusherelement 64 and-teeth 76 to pivot upwardly away from the chain and towithdraw the teeth from engagement with the chain. None of these partswill become jammed and the chain may be advanced fowardly in a loadingdirection until the vehicle is loaded fully. Although the chain isdriven continually past the disengaged teeth 76 of the unloading unit,these parts will not become jammed or damaged. Instead, the teeth 76will chatter as they rest on the moving chain.

When the vehicle is unloaded, the chain is driven in a reversed,unloading direction. As the upper run of the chain begins to moverearwardly the teeth 76 drop immediately into meshing engagement withthe chain and the unloading unit is driven rearwardly with the chain tourge the loads rearwardly toward the exit In addition to the foregoingautomatic engagement and disengagement of the unloading unit 62 itshould be noted that, if desired, the unloading unit 62 may berepositioned along the length of the vehicle bed by simply raising theplate 78 or pushing elements 64 to withdrawthe teeth 76 from engagementwith the chain. The entire unloading unit 62 may be manuallyrepositioned along the chain as desired and then released to enable theteeth 76 to drop downwardly into reengagement with the chain 38.

The downward pivotal movement of the central plate 78 and memberssupported thereon is limited by means of a lower plate 82 which issecured to the lower end of the central plate 78 above the teeth 76which is adapted to abut the upper surface of the rubs 72 on the slide66. The parts are dimensioned so that when the teeth 76 are engagedfully with the chain the weight of the central plate 78 will be borne bythe ribs 72 and not by the chain 38.

FIG. 2 shows the unloading unit when in its most rearward position, suchas at the tail gate of a truck. The extreme rearward position is limitedby means of a rearward stop 84 which is secured to and spans thesprocket supports 52, the stop 84 being disposed at a level at which itmay be engaged by the rearward end of the slide 66. The channel member36 terminates at the forward end of the sprocket supports 52, so thatwhen the unloading unit 62 and slides 66 are in the rearwardmostposition shown, the span 68 of the channel 36 no longer supports theslide 66. When in this position the slide 66 is sup ported by means ofshoulders 86 formed at the upper, inner portions of the sprocketsupports 52. As described above with respect to forward disengagement ofthe unloader unit 62 when the unloader unit 62 is in its rearwardposition, the teeth 76 will not jam with the sprocket 48 or chain 38,but will pivot upwardly out of engagement with the chain. When theunloading unit 62 is in its extreme rearward and disengaged position,continued advancement of the chain in a rearward unloading directionwill not damage the device. The teeth 76 will chatter as they rest onthe rotating rearward sprocket 48 and chain 38.

Loading of the vehicle may be facilitated by a loading unit such as theportable loading bar 88 shown in FIG. 6. The loading bar 88 may beformed simply from a length of pipe 90 or other elongate member to whicha pair of transverse pusher plates 92 are secured. A number ofdownwardly extending teeth 94 are secured to or formed integrally withthe leading end of the pipe 90 and are adapted to be inserted downwardlythrough the registered slots 22, 28 into engagement with the exposedupper run of the chain to drivethe loading bar 88 therewith. The othertrailing end of the loading bar 88 in cludes a downwardly protrudingT-shaped stabilizing slide 96, which extends into the slot 22 and isguided along the slots 22, 28 as the chain 33 drives the loading bar 88forwardly. The stabilizing slide 96 and teeth 94 maintain the bar 88 inalignment with the upper run of the chain. In loading the vehicle withthe loading bar 88, the palletized load or crate is placed on therearward end of the conveyor, as by a fork lift truck, and the loadingbar 88 is placed rearwardly of the load, in the slot 22 with its teeth94 in engagement with the chain 38. The upper run of the chain then isdriven forwardly to urge the loading bar d8 forwardly so that its pusherelements 92 may engage the load and push it forwardly over the bed 12.

in summarizing the operation of the device the chain 38 is driven toposition the unloading unit 62 near the rearward end of the vehicle butallowing space rearwardly of the unloading unit 62 for a palletized loador containerto be placed on the bed so that its forward end is inengagement with the pusher elements 64 of the unloading unit 62. Theloading unit 88 then is connected to the chain 38, rearwardly of theload as described above. The chain 38 then is driven in a forwardloading direction to advance the load into the vehicle. The loadpreferably is advanced only to the extent necessary to provide room atthe rearward end of the bed for placement of a subsequent load. Beforethe subsequent load is placed on the rearward end of the bed the loadingunit 88 is removed. After the subsequent load is placed on the bed theloading bar 88 is again attached to the chain which is againdriven in aloading direction to cause the loading unit to urge both loads forwardlyin the vehicle. The operation continues until the unloading unitadvances to the forward extremity of the chain run at which time it willbe disengaged from the chain. if the vehicle is not then loaded fully,further loading is not precluded. The chain 38 maybe advanced in aloading direction even though the unloading unit is in its most forwardposition.

When unloading the vehicle the chain is driven in a reversed, rearwarddirection which causes reengagement of the unloading unit with the chain38. As the chain and unloading unit are driven rearwardly the loads areurged to the rear of the truck where they may be removed.

it should be appreciated that the foregoing description of my inventionis but a preferred embodiment thereof and it may be modified to suit therequirements of any particular .material handling arrangement. Forexample, the drive member, or chain 38 has been described as beingrecessed beneath the bed 12 of the vehicle. Although, in most instances,this wiil be desirable to protect the chain 38 and to preclude. anytendency for thechain to become jammed against any portion of the load,there may be instances in which the chain may be mounted above the bed12 and will be that the chain will be spaced at alltimes from the loadbeing handled so that it does not interfere with the load.

it should be understood that the foregoing description of my inventionis intended merely to be illustrative thereof and that othermodifications and embodiments will be apparent to those skilled in theart without departing from its spirit.

lclaim: I

l. A material handling device for use with a load carrying vehiclehaving a low-friction bed adapted to facilitate loading and unloadingcomprising: 1

a drive member supported in proximity to said bed, said drive memberbeing movable along a reversible, predetermined path along said bed,said path terminating at forward and rearward extremities;

drive means operatively connected to said drive member to impartreversible movement thereto along said path;

an unloading unit engageable with said drive member for movement inunison therewith along said predetermined path, at least. a portion ofsaid unloading unit being disposed above said bed and being engageablewith a load resting on said bed;

means responsive to positioning of said unloading unit at said forwardextremity of said pathfor disengaging said unloading unit from, saiddrive member thereby terminating said unitary movement of said drivemember and said unloading unit whereby continue advancement of saiddrive member is ineffective to advance said unloading unit; and

means responsive to reversed movement of said drive member to effectreengagement. of said disengaged un loading unit with said drive memberwhereby said unloading unit may be driven rearwardly in unison with saiddrive member.

2. An apparatus as defined in claim 1 wherein said drive membercomprises a chain and wherein said unloading unit includes tooth meansengageable with said chain, said means for disengaging said unloadingunit comprising: means responsive to positioning of said unloading unitat said forward extremity ofsaid path to withdraw said tooth means forengagement with said chain.

3. An apparatus as defined in claim 2 wherein said drive member issupported by means comprising:

a forward idler rotatably mounted to the forward end of said bed;

a rearward idler rotatably mounted to said bed, said forward andrearward idlers comprising said forward and rearward extremities of saidpredetermined path and defining.

4. An apparatus as defined in claim 3 further comprising:

said unloading unit including tooth means extending downwardly therefromtoward and into engagement with said chain;

stop means mounted to said vehicle in proximity to said forward idler;

said unloading unit further including means abuttingly engageably withsaid stop means to limit the extent of forward movement of saidunloading unit; and

means responsive to engagement of said unloading unit with said stopmeans to effect ejection of said tooth means upwardly out of engagementwith said chain.

5. An apparatus as defined in claim 1 further comprising: means mountingsaid unloading unit for sliding movement with respect to said bed andalong said predetermined path.

6. An apparatus as defined in claim 5 wherein said means mounting saidunloading unit for sliding movement along said predetermined pathcomprises:

a slide;

means guiding said slide along said predetermined path; and

means mounting said unloading unit to said slide for movement in unisontherewith along said predetermined path and in a direction transverse tosaid chain and said path to permit disengagement of said unloading unitfrom said chain.

7. An apparatus as defined in claim 6 wherein said drive exposed. inthis modification care should be taken to insure member comprisesachain, said apparatus further comprising:

forward and rearward idler members mounted rotatably to said bed at theforward and rearward ends thereof to guide said chain and defining anupper chain run therebetween;

stop means supported by said bed adjacent said forward idler;

said unloading unit being movable in unison with said chain toward andinto engagement with said stop member, said stop member defining theforward extremity of said upper chain run; and

said means for disengaging said unloading unit from said chaincomprising means responsive to engagement of said unloading unit withsaid stop member to effect said disengagement.

8. An apparatus as defined in claim 7 further comprising:

said unloading unit including tooth means extending downwardly therefromtoward and into engagement with said chain;

said means for disengaging said unloading unit comprising meansresponsive to engagement of said unloading unit with said stop memberfor urging said tooth means out of engagement with said chain.

9. An apparatus as defined in claim 8 wherein said tooth means ismounted to said slide about a pivot disposed rearwardly and above thelevel of the point of engagement of said tooth means with said chain,wherein engagement of said slide with said stop means imparts a momentto said tooth about said pivot to eject said tooth means outwardly fromengagement with said chain.

10. An apparatus as defined in claim 9 further comprising:

means for guiding said run of said chain along said path, said guidemeans including a retaining member having a channel formed therein alongits length to receive slidably and embracingly a portion of said run ofsaid chain, said retaining member being mounted for slidable movementalong said slide and beneath'said bed in unison with said chain run,said retaining member having a portion thereof extending upwardlythrough said slot and said bed, said upper portion having a heightwiseslot being dimensioned to enable said downwardly extending tooth meansof said unloading unit to protrude therethrough into engagement withsaid run of said chain.

11. An apparatus as defined in claim 1 wherein said unloading unitfurther comprises:

a central rib;

said pivot means connecting the rearward end of said central rib to saidslide to enable said central rib to be pivoted upwardly away andtransversely from said chain;

said downwardly extending teeth being formed along the bottom edge ofsaid central rib to enable said teeth to protrude downwardly throughsaid heightwise slot in said slide and into said channel thereof toenable said teeth to engage that portion of the chain run which isembraced within said channel of said slide; and

pusher elements secured to the other, free end of said central rib, saidpusher elements extending transversely of said rib.

12. An apparatus as defined in claim 1 wherein said drive member isrecessed below said bed, said apparatus further comprising:

said bed having a slot formed therein extending along said path; and

said means connecting said unloading unit to said drive member extendingdownwardly through said slot into engagement with said drive member.

13. An apparatus as defined in claim 12 further comprising:

a loading unit completely separable from said drive means,

said loading unit comprising;

an elongate member having a forward end and rearward downwardlytherefrom and being insertable downwardly through said slot in said bedinto engagement with said drive member to enable said loading unit to beadvanced in unison with said drive member;

a stabilizing slide secured to the rearward end of said elongate member,said stabilizing slide having a portion thereof adapted to protrudedownwardly through said slot in said bed to be retained and guided alongsaid slot and predetermined path, said connector means and saidstabilizing slide being effective to maintain said elongate member inalignment with said chain; and

pusher elements secured to said elongate member and extendingtransversely thereof for engagement with a rearward end of a load.

14. An apparatus as defined in claim 1 further comprising:

means responsive to positioning of said unloading unit at said rearwardextremity of said path for disengaging said unloading unit from saiddrive member thereby terminating said unitary movement of said drivemember and said unloading unit whereby continued advancement of saiddrive member in a rearward direction is ineffective to advance saidunloading unit; and

means responsive to reversed movement of said drive member in a forwarddirection to effect reengagement of said disengaged unloading unit withsaid drive member at said rearward extremity of said path whereby saidunloading unit may be driven forwardly in unison with said drive member.

1. A material handling device for use with a load carrying vehiclehaving a low-friction bed adapted to facilitate loading and unloadingcomprising: a drive member supported in proximity to said bed, saiddrive member being movable along a reversible, predetermined path alongsaid bed, said path terminating at forward and rearward extremities;drive means operatively connected to said drive member to impartreversible movement thereto along said path; an unloading unitengageable with said drive member for movement in unison therewith alongsaid predetermined path, at least a portion of said unloading unit beingdisposed above said bed and being engageable with a load resting on saidbed; means responsive to positioning of said unloading unit at saidforward extremity of said Path for disengaging said unloading unit fromsaid drive member thereby terminating said unitary movement of saiddrive member and said unloading unit whereby continue advancement ofsaid drive member is ineffective to advance said unloading unit; andmeans responsive to reversed movement of said drive member to effectreengagement of said disengaged unloading unit with said drive memberwhereby said unloading unit may be driven rearwardly in unison with saiddrive member.
 2. An apparatus as defined in claim 1 wherein said drivemember comprises a chain and wherein said unloading unit includes toothmeans engageable with said chain, said means for disengaging saidunloading unit comprising: means responsive to positioning of saidunloading unit at said forward extremity of said path to withdraw saidtooth means for engagement with said chain.
 3. An apparatus as definedin claim 2 wherein said drive member is supported by means comprising: aforward idler rotatably mounted to the forward end of said bed; arearward idler rotatably mounted to said bed, said forward and rearwardidlers comprising said forward and rearward extremities of saidpredetermined path and defining.
 4. An apparatus as defined in claim 3further comprising: said unloading unit including tooth means extendingdownwardly therefrom toward and into engagement with said chain; stopmeans mounted to said vehicle in proximity to said forward idler; saidunloading unit further including means abuttingly engageably with saidstop means to limit the extent of forward movement of said unloadingunit; and means responsive to engagement of said unloading unit withsaid stop means to effect ejection of said tooth means upwardly out ofengagement with said chain.
 5. An apparatus as defined in claim 1further comprising: means mounting said unloading unit for slidingmovement with respect to said bed and along said predetermined path. 6.An apparatus as defined in claim 5 wherein said means mounting saidunloading unit for sliding movement along said predetermined pathcomprises: a slide; means guiding said slide along said predeterminedpath; and means mounting said unloading unit to said slide for movementin unison therewith along said predetermined path and in a directiontransverse to said chain and said path to permit disengagement of saidunloading unit from said chain.
 7. An apparatus as defined in claim 6wherein said drive member comprises a chain, said apparatus furthercomprising: forward and rearward idler members mounted rotatably to saidbed at the forward and rearward ends thereof to guide said chain anddefining an upper chain run therebetween; stop means supported by saidbed adjacent said forward idler; said unloading unit being movable inunison with said chain toward and into engagement with said stop member,said stop member defining the forward extremity of said upper chain run;and said means for disengaging said unloading unit from said chaincomprising means responsive to engagement of said unloading unit withsaid stop member to effect said disengagement.
 8. An apparatus asdefined in claim 7 further comprising: said unloading unit includingtooth means extending downwardly therefrom toward and into engagementwith said chain; said means for disengaging said unloading unitcomprising means responsive to engagement of said unloading unit withsaid stop member for urging said tooth means out of engagement with saidchain.
 9. An apparatus as defined in claim 8 wherein said tooth means ismounted to said slide about a pivot disposed rearwardly and above thelevel of the point of engagement of said tooth means with said chain,wherein engagement of said slide with said stop means imparts a momentto said tooth about said pivot to eject said tooth means outwardly fromengagement with said chain.
 10. An apparatus as defined in claim 9further comprising: means for guiding said run of said chain along saidpath, said guide means including a retaining member having a channelformed therein along its length to receive slidably and embracingly aportion of said run of said chain, said retaining member being mountedfor slidable movement along said slide and beneath said bed in unisonwith said chain run, said retaining member having a portion thereofextending upwardly through said slot and said bed, said upper portionhaving a heightwise slot being dimensioned to enable said downwardlyextending tooth means of said unloading unit to protrude therethroughinto engagement with said run of said chain.
 11. An apparatus as definedin claim 1 wherein said unloading unit further comprises: a central rib;said pivot means connecting the rearward end of said central rib to saidslide to enable said central rib to be pivoted upwardly away andtransversely from said chain; said downwardly extending teeth beingformed along the bottom edge of said central rib to enable said teeth toprotrude downwardly through said heightwise slot in said slide and intosaid channel thereof to enable said teeth to engage that portion of thechain run which is embraced within said channel of said slide; andpusher elements secured to the other, free end of said central rib, saidpusher elements extending transversely of said rib.
 12. An apparatus asdefined in claim 1 wherein said drive member is recessed below said bed,said apparatus further comprising: said bed having a slot formed thereinextending along said path; and said means connecting said unloading unitto said drive member extending downwardly through said slot intoengagement with said drive member.
 13. An apparatus as defined in claim12 further comprising: a loading unit completely separable from saiddrive means, said loading unit comprising; an elongate member having aforward end and rearward end; connector means secured to said leadingend of said elongate member, said connector means extending downwardlytherefrom and being insertable downwardly through said slot in said bedinto engagement with said drive member to enable said loading unit to beadvanced in unison with said drive member; a stabilizing slide securedto the rearward end of said elongate member, said stabilizing slidehaving a portion thereof adapted to protrude downwardly through saidslot in said bed to be retained and guided along said slot andpredetermined path, said connector means and said stabilizing slidebeing effective to maintain said elongate member in alignment with saidchain; and pusher elements secured to said elongate member and extendingtransversely thereof for engagement with a rearward end of a load. 14.An apparatus as defined in claim 1 further comprising: means responsiveto positioning of said unloading unit at said rearward extremity of saidpath for disengaging said unloading unit from said drive member therebyterminating said unitary movement of said drive member and saidunloading unit whereby continued advancement of said drive member in arearward direction is ineffective to advance said unloading unit; andmeans responsive to reversed movement of said drive member in a forwarddirection to effect reengagement of said disengaged unloading unit withsaid drive member at said rearward extremity of said path whereby saidunloading unit may be driven forwardly in unison with said drive member.